1. Field of the Invention
This invention relates to a stable calcium hypochlorite composition which decomposes little even when left in storage over a long period and at a high temperature and also relates to a method for the preparation of the composition.
2. Description of the Prior Art
Calcium hypochlorite is a strong oxidizing agent and is an important compound being widely in use for treatment of water of swimming pools, water supplies and swerages and also for bleaching cotton and pulp on account of the excellent sterilizing and bleaching effects obtainable therefrom.
A composition which is generally known by the name of "high test hypochlorite" and is commercially available is composed of calcium hypochlorite as its main constituent having 60 wt %, 65 wt % or 70 wt % of available chlorine content.
The calcium hypochlorite composition is mostly used for sterilization of the water of swimming pools and the season during which it is used for that purpose is summertime. Accordingly, the temperature at which it is transported or stored sometimes exceeds 40.degree. C. Therefore, it is generally desired to obtain a stable calcium hypochlorite composition in which the calcium hypochlorite decomposes little at a high temperature.
To meet this requirement, there is available a calcium hypochlorite composition which is virtually anhydrous. However, this anhydrous calcium hypochlorite composition tends to suddenly decompose when it is brought into contact with flames, sparks and organic matters. In other words, it tends to explode and requires much caution in handling it. Further, it cannot be easily handled because it produces much dust. Another disadvantage lies in that it necessitates the use of much energy for dehydration of it during the manufacture thereof. These disadvantages can be eliminated by allowing it to keep a high water content therein. However, it is well known that the stability of the calcium hypochlorite decreases as the water content increases in the calcium hypochlorite composition.
To solve this problem, many attempts have been made to obtain a stable calcium hypochlorite composition having a high water content.
For example, a U.S. Pat. No. 3,793,216 (corresponding to a Japanese patent application laid open No. 48-65183) has proposed a calcium hypochlorite composition which is prepared by adding a water soluble inorganic hydrate to a calcium hypochlorite to make a water content thereof 3 to 13 wt %. Further, a Japanese patent application laid open No. 51-111497 has proposed a calcium hypochlorite composition which is prepared by mixing a calcium hypochlorite having 16 to 22 wt % of water content with a virtually anhydrous calcium hypochlorite having its water content not exceeding 2 wt % and which is arranged to have at least 50 wt % of available chlorine included therein.
However, the methods employed by these prior arts are not only uneconomical because they require the addition of an expensive water-soluble inorganic hydrate or the use of two kinds of calcium hypochlorite composite of different compositions, but also, they do not give stable products according to the results of the studies conducted by the present inventors. They examined the effects of the water content and temperature on the stability of a calcium hypochlorite composition to find that, with the decomposition of calcium hypochlorite which takes place in a composite having 2 to 3 wt % of water content at a temperature of 20.degree. C. used as reference, the degree of its decomposition increases by about four times at 40.degree. C. In case where the water content is arranged to be 5 to 6 wt %, the decomposition increases by 7 to 8 times at 40.degree. C. When the water content exceed 7 wt % at 40.degree. C., the decomposition increases at least by 10 times and the composition completely loses its value as commercial product.
The inventors further conducted their study based on this finding in an effort to find a calcium hypochlorite composition which remains stable even at a high water content and at a high temperature. As a result of this study, they have found that a calcium hypochlorite composition having a high calcium hypochlorite content can be greatly stabilized when it contains at least 5 wt % of calcium hydroxide and 5 wt % or less than that of calcium chloride and when it has at least 4 wt % of water content and thus came to complete the present invention.